The present invention relates to a compound having a pyrrole ring and a light-emitting device comprising the compound.
Recently, various display devices have been widely studied. In particular, light-emitting devices including organic EL devices are advantageous in that they can emit light with high luminance by lowered applying voltage, whereby much attention has been paid thereto.
For example, a light-emitting device comprising organic thin layers, which are provided by vapor-depositing organic compounds, has been disclosed in Applied Physics Letters, 51, 913 (1987). This light-emitting device has a structure where an electron-transporting layer and a hole-transporting layer are laminated between electrodes, to exhibit more excellent light-emitting properties than that of conventional devices having a single-layer structure. In this light-emitting device, N,Nxe2x80x2-di-m-tolyl-N,Nxe2x80x2-diphenylbenzidine (TPD) is used as a hole-transporting material for the hole-transporting layer. TPD is a typical example of triarylamine derivatives known as an effective hole-transporting material. However, the triarylamine derivatives are generally high in crystallinity, whereby light-emitting devices using the derivatives are generally poor in durability during storage and driving. Further, although the organic thin layers are desirably provided by a coating method from viewpoints of simplification of production processes, improvement of workability, increasing the light-emitting device in size, etc., the triarylamine derivatives is poor in solubility in an organic solvent to be not suitable for the coating method. Additionally, the inventor has found that light-emitting devices comprising polymerized triarylamine derivatives exhibit insufficient light-emitting properties.
Under such a circumstance, research is in progress for light-emitting devices using nitrogen-containing heterocyclic compounds such as a carbazole derivative instead of the triarylamine derivatives as the hole-transporting material. For example, various low molecular weight carbazole derivatives and poly-N-vinylcarbazole derivatives usable as the hole-transporting material are disclosed in Preprints of the 6th Seminar on Molecular Electronics and Bioelectronics Subcommittee of The Japan Society of Applied Physics, 1997. However, the light-emitting devices using such a hole-transporting material are poor in light-emitting efficiency and require high applying voltage for light emission.
An object of the present invention is to provide a compound usable for a light-emitting device that can emit light with high luminance and excellent light-emitting efficiency, and a light-emitting device comprising the compound.
As a result of intense research in view of the above object, the inventor has found that a light-emitting device using a particular compound having a pyrrole ring emits light with high luminance and excellent light-emitting efficiency. The present invention has been accomplished by the finding.
Thus, a compound of the present invention is represented by the following general formula (1): 
wherein R1 represents a hydrogen atom or a methyl group; R2 and R3 independently represent a hydrogen atom or a substituent and may bond together to form a ring; R4 represents a hydrogen atom or a substituent selected from the group consisting of alkyl groups, alkenyl groups, alkynyl groups, aryl groups, heterocyclic groups, alkylcarbonyl groups, arylcarbonyl groups, alkylsulfonyl groups, arylsulfonyl groups, alkoxycarbonyl groups, aryloxycarbonyl groups, carbamoyl groups and sulfamoyl groups; Z represents an atomic group forming an aromatic ring; A represents a comonomer unit; and k and n each represent a mole fraction, k being 1 to 100 (%), n being 0 to 99 (%), and the sum of k and n is 100 (%).
In the compound of the present invention, A in the general formula (1) is preferably derived from a comonomer selected from the group consisting of styrene, xcex1-methylstyrene, butadiene, vinyl acetate, vinyl carbazole, acrylic acid, methacrylic acid, acrylic esters, methacrylic esters, acrylamide and methacrylamide. The aromatic ring formed by Z is particularly preferably a benzene ring. The compound preferably has a weight-average molecular weight (Mw) of 1,000 to 10,000,000.
It is particularly preferred that the compound of the present invention is further represented by the following general formula (2): 
wherein R1 represents a hydrogen atom or a methyl group; R4 represents a hydrogen atom or a substituent selected from the group consisting of alkyl groups, alkenyl groups, alkynyl groups, aryl groups, heterocyclic groups, alkylcarbonyl groups, arylcarbonyl groups, alkylsulfonyl groups, arylsulfonyl groups, alkoxycarbonyl groups, aryloxycarbonyl groups, carbamoyl groups and sulfamoyl groups; R5 and R6 independently represent a substituent; p represents an integer of 1 to 4; q represents an integer of 1 to 3; A represents a comonomer unit; and k and n independently represent a mole fraction, k being 1 to 100 (%), n being 0 to 99 (%), and the sum of k and n is 100 (%).
In the compound represented by the general formula (2), a carbon atom having R1 preferably bonds to 3-position of a carbazole ring.
A light-emitting device of the present invention comprises a pair of electrodes and one or more organic layers disposed therebetween, wherein at least one of the organic layers comprises the above-mentioned compound of the present invention. Weight ratio of the compound is preferably 0.01 to 99.9 weight % based on the total weight of the organic layer comprising the compound. It is preferable that at least one of the organic layers is provided by a coating method. Further, at least one of the organic layers preferably comprises a light-emitting material that utilizes a triplet exciton for light emission, and the light-emitting material is preferably an iridium complex.